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  <div class="section" id="module-crypt">
<h1>36.5. <tt class="xref docutils literal"><span class="pre">crypt</span></tt> &#8212; Function to check Unix passwords<a class="headerlink" href="#module-crypt" title="Permalink to this headline">¶</a></h1>
<p><em>Platforms: </em>Unix</p>
<p id="index-246">This module implements an interface to the <em>crypt(3)</em> routine, which is
a one-way hash function based upon a modified DES algorithm; see the Unix man
page for further details.  Possible uses include allowing Python scripts to
accept typed passwords from the user, or attempting to crack Unix passwords with
a dictionary.</p>
<p id="index-247">Notice that the behavior of this module depends on the actual implementation  of
the <em>crypt(3)</em> routine in the running system.  Therefore, any
extensions available on the current implementation will also  be available on
this module.</p>
<dl class="function">
<dt id="crypt.crypt">
<tt class="descclassname">crypt.</tt><tt class="descname">crypt</tt><big>(</big><em>word</em>, <em>salt</em><big>)</big><a class="headerlink" href="#crypt.crypt" title="Permalink to this definition">¶</a></dt>
<dd><p><em>word</em> will usually be a user&#8217;s password as typed at a prompt or  in a graphical
interface.  <em>salt</em> is usually a random two-character string which will be used
to perturb the DES algorithm in one of 4096 ways.  The characters in <em>salt</em> must
be in the set <tt class="docutils literal"><span class="pre">[./a-zA-Z0-9]</span></tt>.  Returns the hashed password as a string, which
will be composed of characters from the same alphabet as the salt (the first two
characters represent the salt itself).</p>
<p id="index-248">Since a few <em>crypt(3)</em> extensions allow different values, with
different sizes in the <em>salt</em>, it is recommended to use  the full crypted
password as salt when checking for a password.</p>
</dd></dl>

<p>A simple example illustrating typical use:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">crypt</span><span class="o">,</span> <span class="nn">getpass</span><span class="o">,</span> <span class="nn">pwd</span>

<span class="k">def</span> <span class="nf">login</span><span class="p">():</span>
    <span class="n">username</span> <span class="o">=</span> <span class="nb">raw_input</span><span class="p">(</span><span class="s">&#39;Python login:&#39;</span><span class="p">)</span>
    <span class="n">cryptedpasswd</span> <span class="o">=</span> <span class="n">pwd</span><span class="o">.</span><span class="n">getpwnam</span><span class="p">(</span><span class="n">username</span><span class="p">)[</span><span class="mf">1</span><span class="p">]</span>
    <span class="k">if</span> <span class="n">cryptedpasswd</span><span class="p">:</span>
        <span class="k">if</span> <span class="n">cryptedpasswd</span> <span class="o">==</span> <span class="s">&#39;x&#39;</span> <span class="ow">or</span> <span class="n">cryptedpasswd</span> <span class="o">==</span> <span class="s">&#39;*&#39;</span><span class="p">:</span>
            <span class="k">raise</span> <span class="s">&quot;Sorry, currently no support for shadow passwords&quot;</span>
        <span class="n">cleartext</span> <span class="o">=</span> <span class="n">getpass</span><span class="o">.</span><span class="n">getpass</span><span class="p">()</span>
        <span class="k">return</span> <span class="n">crypt</span><span class="o">.</span><span class="n">crypt</span><span class="p">(</span><span class="n">cleartext</span><span class="p">,</span> <span class="n">cryptedpasswd</span><span class="p">)</span> <span class="o">==</span> <span class="n">cryptedpasswd</span>
    <span class="k">else</span><span class="p">:</span>
        <span class="k">return</span> <span class="mf">1</span>
</pre></div>
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